| Crossover Design: |
| As mentioned earlier, Ashley's concern for the difficulty of blending an 8 inch woofer and a 1 inch soft dome tweeter in a high quality two-way design pushed her to a lower than usual high-pass frequency, 2000Hz. The published Fs for the Dayton #275-070 tweeter is about 900 Hz, so 2000 Hz seemed o.k. Unfortunately, impedance sweeps of 10 of these tweeters revealed all were 150 to 400 Hz higher at Fs than published. The best pair (lowest Fs) were selected for Ashley's speakers. She disdained any of the modifications others (including me) have made to these tweeters in search of lower Fs. We predicted and then measured some resonance in the tweeter crossed over at 2000 Hz, even third order. It was decided to incorporate impedance resonance compensation on the tweeters (more commonly done with woofers, I believe). So, with Zobels on both drivers and with additional filtration on the tweeter and with a 4 dB L-Pad (tweeter) and all within a 3rd order Butterworth network, Ashley constructed the crossover networks depicted in the screen capture below: |
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| Components: Inductors: L2: 14 gauge air core (or 16 gauge air core hand wound) L1: 20 gauge bobbin core L3: 18 gauge air core LM: 18 gauge air core Capacitors: All non-polar electrolytics except film & foil bypasses on C1 and C2 Most capacitances achieved by summing smaller values in parallel. Resistors: Sand Cast wire wound Non-inductive when in series with tweeter (Rp1) and when only value available Connections: Direct lead to lead soldering when possible, 16 guage magnet wire elsewhere. Above board leads are color coded 16 gauge hookup wire. Topology: Note that the high and low pass sections are separate so that biamplification and/or biwiring is possible. |